Table of Contents

Linux

Linux Distribution

-A Linux distribution is comprised of the Linux kernel and additional software

- https://DistroWatch.com
- Red Hat Enterprise Linux (RHEL)
- Fedora
- Ubuntu
- Debian
- SuSE Linux Enterprise Server (SLES)
- OpenSuSE

Ways to Get Access to Linux

  • Web Based Command Line Access
  • Web Hosting Shell Accounts
  • VPS (Virtual Private Server) or Cloud Server
  • Live Linux Distro
  • Install on Hardware
  • Use Preinstalled Images with VirtualBox

Getting Connected

  • If you have physical access or if the Linux system is running in a VM, log in directly.
  • To log in over the network use SSH.
    • SSH replace "telnet"
  • PuTTY is a Windows SSH client.
  • The command line utility ssh is used in Mac
  • Detailed Instructions

Directory Structure

  • Common Directories
    • /: “Root,” the top of the file system hierarchy.
    • /bin: Binaries and other executable programs.
    • /etc: System configuration files.
    • /home: User home directories.
    • /opt: Optional or third party software.
      • e.g. Google Earth
    • /tmp: Temporary space, typically cleared on reboot.
    • /usr: User related programs.
    • /var: Variable data, most notably log files.
      • For example, /var/logs
  • Applications that are not part of the base OS can be installed in:
    • /usr/local
    • /opt
  • Comprehensive Directory Listing

The Shell

  • The shell is the default user interface.
  • Use the terminal application to get to the CLI.
  • Shell prompts can vary greatly in appearance.
    • jason@linuxsvr ~]$ normal user
    • [root@linuxsvr:~]# super user
    • Tilde Expansion:
      • ~jason = /home/jason
      • ~pat = /home/pat
      • ~root = /root
      • ~ftp = /srv/ftp
  • Root is the superuser.
  • Server distributions do not include GUIs

Basic Linux Commands

  • ls: Lists directory contents. -l: long listing format
  • cd: Changes the current directory.
    • cd (with no arguments): Back to home directory
  • pwd: Displays the present working directory.
  • cat: Concatenates and displays files.
  • echo: Displays arguments to the screen.
  • man: Displays the built-in manual.
    • man -k calendar: search manual pages using keyword
    • Move around man pages:
      • space: display the next page
      • enter: move down one line
      • g: go to top of page
      • G: go to bottom of page
      • q: quit
  • touch: Craete new file or update time stamp of existing file
  • exit: Exits the shell or your current session.
  • clear: Clears the screen.
  • Ask commands for help with --help or -h

Environment Variables

  • For example, $PATH controls your search path
    • echo $PATH: view content of \$PATH variable
  • To execute commands outside of \$PATH:
    • /full/path/to/command
    • ./command-in-this-dir
  • which cat: locate the command cat

Working with Directories

  • Directories Shortcuts
    • . This directory
    • .. The parent directory
    • cd - Change to the previous directory
    • pwd Show present working directory
  • echo $OLDPWD: view directory you pervious end
  • Create and Remove Directories
    • mkdir [-p] directory
      • use -p to create multiple directories
    • rmdir [-p] directory
      • Only remove empty directories
    • rm -rf directory
      • Recursively removes directories

Listing Files ('ls' command)

  • ls -l: Show long listing format

    -rw-rw-r-- 1 jason users 10400 Sep 27 08:52 sales.data

    • Permissions: -rw-rw-r--
    • Number of links: 1
    • Owner name: jason
    • Group name: users
    • Number of bytes in the file: 10400
    • Last modification time: Sep 27 08:52
    • File name: sales.data
  • ls -a: Show hidden files
    • Hidden files are not displayed by default
    • Hidden files begins with a period .
    • Sometimes called "dot files"
  • Command options can be combined
    • ls -l -a is the same as ls -la and ls -al
  • ls -F: Show file types (at the end)
    • /: Directory
    • @: Link
    • *: Executable
  • ls -t: List file by time
  • ls -r: Reverse order
  • ls -latr: Long listing including all files reverse sorted by time
  • ls -R: List files recursively
    • The tree command is similar to ls -R but creates visual output. The command may not be installed by default
      • tree -d: List directories only
      • tree -C: Colorize output
  • ls --color: Colorize the output

Working with Spaces in Names

  • Just say no to spaces!
  • Alternatives:
    • Hyphens -
    • Underscore _
    • CamelCase
  • Encapsulate the entire file name in quotes
    • ls -l "my notes.txt" or ls -l 'my notes.txt'

File & Directory Permissions

  • Type

    • $ls -l

      -rw-rw-r-- 1 jason users 10400 Sep 27 08:52 sales.data

Symbol Type
- Regular file
d Directory
\ Symbolic link
r Read
w Write
x Execute
  • Permissions - File vs Directories
    • Permissions on a directory can effect the files in the directory
    • If the file permission looks correct, start checking directory permissions
    • Work you way up to the root
Permission File Directory
Read (r) Allows a file to be read. Allows file names in the directory to be read.
Write (w) Allows a file to modified. Allows entries to be modified within the directory.
Execute (x) Allows the execution of a file Allows access to contents and metadata for entries.

  • Permission Categories

    • u: User
    • g: Group
    • o: Other
    • a: All

  • Groups

    • Every user is in at least one group.
    • Users can belong to many groups.
    • Groups are used to organize users.
    • The groups [userId] command displays a user’s groups.
    • You can also use id -Gn

img

  • Changing Permissions

    • chmod: Change mode (permission) command
      • chmod g+w sales.data
      • chmod g-w sales.data
      • chmod g+wx sales.data
      • chmod u+rwx, g-x sales.data
      • chmod a=r sales.data
      • chmod u=rwx, g=rx, o= sales.data
        • Remove all permissions from others
    • ugoa: User category
      • user, group, other, all
    • +-=: Add, subtract or set permissions
    • rwx: Read, Write, Execute

  • Numeric Based Permissions

r w x
0 0 0 Value for off
1 1 1 Binary value for on
4 2 1 Base 10 value for on

img

  • Order has meaning
    • For example, chmod 754 sales.data

img

  • Commonly Used Permissions
    • Avoid using 666 or 777

img

  • Working with Groups

    • When you create a file, new file belong to your primary group
    • The chgrp command changes the group
      • chgrp sales sales.data

  • File Creation Mask

    • File creation mask determines default permissions.
    • If no mask were used permissions would be:
      • 777 for directories
      • 666 for files

  • The umask Command

    • Turns off/ takes away permissions
    • Syntax: umask [-S] [mode]
      • -S: return symbolic notation
        • umask -S returns u=rwx, g=rx, o=rx for .
      • mode: octal value '755', '664' etc

    • Octal subtraction

      • Note: it's just an estimate img

    • Common umask modes

      • 022
      • 002
      • 077
      • 007 img
    • Special Modes
      • If you run umask without any arguments, it will display the mode in 4 characters instead of the 3 that we're working with:
        • umask returns 0022 (same as umask 022)
      • The additional character is the special modes:
        • setuid
        • setgid
        • sticky
      • These speical modes are not coverd in this course

View Files & the Nano Editor

  • Displaying Contents of Static Files

    • cat file: Display the contents of file.
    • more file: Browse through a text file.
    • less file: More features than more (less is more).
    • head file: Output the beginning (or top) portion of file.
      • Displays only 10 lines by default
      • Change this behavior with -n e.g. head -15 file.txt
    • tail file: Output the ending (or bottom) portion of file.
      • Displays only 10 lines by default
      • Change this behavior with -n e.g. tail -15 file.txt

  • Viewing Files in Real Time

    • tail -f file: Displays data as it is being written to the file e.g. log file

  • Nano Editor

    • Nano is a simple editor.
    • Easy to to learn.
    • Not as advanced as vi or emacs.
    • If nano isn't available, look for pico.
    • nano file.txt

Editing Files in Vi

  • Has advanced and powerful features
  • Not intuitive
  • Harder to learn than nano
  • Requires a time investment
  • vi [file]: Edit file
  • vim [file]: Same as vi, but more features
    • 'vim' stands for vi improved with syntax highlighting and ability to edit file over the network
    • On many linux distributions, when you type 'vi', you're actually running 'vim'
  • view [file]: Starts vim in read-only mode
  • Advantages on using vi:
    • Always available on a Linux system
    • Once you learn the key mapping on vi, you can apply them to other commands, like 'man', 'more', 'less', 'view' or edit shell commands
  • Vi has 3 modes:
Mode Key
Command Esc
Insert iIaA
Line :

  • Vi Command Mode and Navigation

    • When vi starts, it's in command mode
    • The other 2 modes: Insert and Line modes
    • To get back to command mode, hit the esc key
    • Navigation keys:
      • k: Up one line.
      • j: Down one line.
      • h: Left one character.
      • l: Right one character. img
      • w: Right one word.
      • b: Left one word.
      • ^ Go to the beginning of the line.
      • $: Go to the end of the line.

  • Vi Insert Mode

    • To use vi Insert Mode, use either one of the 4 keys below:
      • i: Insert at the cursor position.
      • I: Insert at the beginning of the line.
      • a: Append after the cursor position.
      • A: Append at the end of the line.

  • Vi Line Mode

    • To use vi Line Mode, type colon :
      • :w: Writes (saves) the file.
      • :w!: Forces the file to be saved.
      • :q: Quit.
      • :q!: Quit without saving changes.
      • :wq!: Write and quit.
      • :x: Same as :wq.
      • :n: Positions the cursor at line n.
        • :15: Go to line 15 of the file
      • :$: Positions the cursor on the last line.
      • :set nu: Turn on line numbering.
      • :set nonu: Turn off line numbering.
      • :help [subcommand] Get help.

  • Vi Repeating Commands

    • Repeat a command by preceding it with a number.
      • 5k: Move up a line 5 times
      • 80i<Text><ESC>: Insert 80 times
      • 80i_<Esc>: Insert 80 "_" characters

  • Vi Deleting Text

    • In command mode
    • x: Delete a character.
    • dw: Delete a word.
    • dd: Delete a line.
    • D: Delete the remaining text from the current position.

  • Vi Changing Text

    • r: Replace the current character.
    • cw: Change the current word.
    • cc: Change the current line.
    • c$: Change the text from the current position.
    • C: Same as c$.
    • ~: Reverses the case of a character.

  • Vi Copy and Paste

    • yy: Yank (copy) the current line.
    • y<position>: Yank the .
      • yw: Yank a word
      • y3w: Yank three words
    • p: Paste the most recent deleted or yanked text.

  • Vi Undo/ Redo

    • u: Undo
    • Ctrl-R: Redo

  • Vi Searching

    • /<pattern>: Start a forward search.
    • ?<pattern>: Start a reverse search.
    • n: Go to the next match
    • N: Go to the previous match

  • Vi Tutor

    • vimtutor: VIM Tutor

Vi Cheat Sheet

Editing Files with Emacs

  • Emacs is Powerful editor.
  • Some people prefer vi, other emacs.
  • Either are great editors.
  • Use what feels comfortable to you.
  • Emacs Keys:
    • emacs [file]: Edit file.
    • C-<char>: Ctrl while pressing <char>.
    • M-<char>: "Meta" key (alt key) while pressing <char>.
    • M-<char>: Esc, then type
  • Emacs Commands:
    • C-h: Help
    • C-x C-c: Exit
    • C-x C-s: Save the file
    • C-h t: Built-in tutorial
    • C-h k <key>: Describe key

  • Emacs Navigation:

    • C-p: Previous line.
    • C-n: Next line.
    • C-b: Backward one character.
    • C-f: Forward one character.
    • M-f: Forward one word.
    • M-b: Backward one word.
    • C-a: Go to the beginning of the line.
    • C-e: Go to the end of the line.
    • M-<: Go to the beginning of the file.
    • M->: Go to the end of the file.

  • Emacs Deleting Text

    • C-d: Delete a character.
    • M-d: Delete a word.

  • Emacs Copy & Paste, Undo

    • C-k: Kill (cut)
    • C-y: Yank (paste)
    • C-x u: Undo

  • Emacs Searching

    • C-s: Start a forward search.
    • C-r: Start a reverse search.

  • Emacs Repeating Commands

    • C-u N <command>: Repeat <command> N times.

Emacs Cheat Sheet

Finding Files & Directories

  • The find Command

    • Syntax: find [path...] [expression]
    • Recursively finds files in path that match expression.
    • Results are in real time
    • If no arguments are supplied it find all files in the current directory (includes hidden files).
    • Options:
      • -name pattern: Find files and directories that match 'pattern'.
      • -iname pattern: Like '-name', but ignores case.
      • -ls: Performs an 'ls' on each of the found items.
      • -mtime days: Finds files that are 'days' old.
      • -size num: Finds file that are of size 'num'.
      • -newer file: Finds files that are newer than 'file'.
      • -exec command {} \;: Run 'command' against all the files that are found.
    • Examples:
      • find /bin -name *v
      • find . -mtime +10 -mtime -13: find files that are more than 10 days old but less than 13 days old in current directory
      • find s* -ls
      • find . -size +1M: find files that are more than 1MB
        • 1K: 1 Kilobyte
        • 1G: 1 Gigabyte
      • find . -type d -newer file.txt: find directories that are newer than 'file.txt'
      • find . -exec file {} \;: excute 'file' command on all search result
        • The file command tells you the file type

  • A Fast Find - Locate

    • Syntax locate pattern
    • Lists files that match pattern.
    • Faster than the find command.
    • Queries an index.
      • Typically an index is re-build everyday
    • Results are not in real time.
    • May not be enabled on all systems.

Graphical Editors

  • Various graphical editors exist for Linux.
    • If you are running Linux in a desktop operating system
    • Not available via SSH or terminal emulator applications
    • emacs: Emacs has a graphical mode too.
    • gedit: The default text editor for Gnome.
    • gvim: The graphical version of vim.
    • kedit: The default text editor for the KDE.
    • AbiWord: Microsoft Word alternative.
    • LibreOffice: Full office suite.
      • Found under Application > Office
    • Kate: Source code editor.
  • Graphical modes exist for emacs and vi.
    • Found under Applications > Accessories

Deleting, Copying, Moving and Renaming Files

  • Removing Files

    • It's a good idea to use ls command to check file to be remove before acutally removing it

    • rm file: Remove file.

    • rm -r dir: Remove the directory and its contents recursively.
    • rm -f file: Force removal and never prompt for confirmation.

  • Copying Files

    • cp source_file destination_file: Copy source_file to destination_file.
    • cp src_file1 [src_fileN ...] dest_dir: Copy source_files to destination_directory.
    • cp -i: Run in interactive mode.
      • With prompt to overwrite the file if same file exists in destination
    • cp -r source_directory destination: Copy src_directory recursively to destination.
      • If destination directory does not exist, it will create the new directory

  • Moving and Renaming Files

    • mv: Move or rename files and directories.
    • mv source destination
    • mv -i source destination: Interactive mode

  • Sorting Data

    • sort file: Sort text in file.
    • Options:
      • -k F: Sort by key. F is the field number.
        • sort -u -k2 more-secrets: sort by the second column in file 'more-secrets'
      • -r: Sort in reverse order.
      • -u: Sort unique.
        • Removes duplicate lines and output unique results

  • Creating Archives (tar)

    • tar [-] c|x|t f tarfile [pattern]
    • Create, extract or list contents of a tar archive using pattern, if supplied.
    • Unlike other commands, tar doesn't need the hyphen - before options
    • Options:
      • c: Create a tar archive.
      • x: Extract files from the archive.
      • t: Display the table of contents (list).
      • v: Be verbose.
      • z: Use compression.
      • f file: Use this file.
    • Examples:
      • tar cf tps.tar tpsreports
      • tar tf tps.tar
      • tar xf /home/test/tps.tar: extract files
      • tar xvf /home/test/tps.tar: extract files in verbose

  • Compressing Files to Save Space

    • gzip: Compress files.
      • Add extension .gz in the file name
    • gunzip: Uncompress files.
    • gzcat or zcat: Concatenates compressed files.

  • Using gzip + tar

    • tar zcf test.tgz tpsreports: Compress tar
    • tar zcf test.tar.gz tpsreports: Compress tar
      • Note the naming convention tgz, tar.gz
    • tar ztvf tpsreports: View contents of gzip files
  • Disk Usage
    • du: Estimates file usage.
    • du -k: Display sizes in Kilobytes.
    • du -h: Display sizes in human readable format.

Wildcards

  • A character or string used for pattern matching.
  • Globbing expands the wildcard pattern into a list of files and/or directories (paths)
  • Wildcards can be used with most commands.
    • ls
    • rm
    • cp
  • *: matches zero or more characters.
  • ?: matches exactly one character.
  • []: A character class.
    • Matches any of the characters included between the brackets. Matches exactly one character.
    • [aeiou]: start with a vowel
    • ca[nt]*
      • can
      • cat
      • candy
      • catch
  • [!]: Matches any of the characters NOT included between the brackets. Matches exactly one character.
    • [!aeiou]*: NOT starts with a vowel
      • baseball
      • cricket

  • Wildcards Ranges

    • Use two characters separated by a hyphen - to create a range in a character class.
      • [a-g]*
        • Matches all files that start with a, b, c, d, e, f, or g.
      • [3-6]*
        • Matches all files that start with 3, 4, 5 or 6.

    • Predefined named character classes

      • [[:alpha:]]: Matches alphabetical letters (upper and lower cases letters)
      • [[:alnum:]]: Matches alpha numeric characters
      • [[:digit:]]
        • ls *[[:digit:]]: find files that end with a digit
      • [[:lower:]]

      • [[:space:]]: Matches spaces, tabs, new line characters

      • [[:upper:]]

  • Matching Wildcard Patterns

    • \: escape character. Use if you want to match a wildcard character.
    • Match all files that end with a question mark:
      • *\?
      • found 'done?'

Input, Output (I/O) and Redirection

I/O Name Abbreviation File Descriptor
Standard Input stdin 0
Standard Output stdout 1
Standard Error stderr 2
  • stderr: 'ls: cannot access not-here: No such file or directory'
  • stdout: 'files.txt'

  • Redirection

    • >: Redirects standard output to a file.
      • Overwrites (truncating) existing contents.
      • ls -l 1> files.txt is the same as ls -l > files.txt
    • >>: Redirects standard output to a file.
      • Appends to any existing contents.
    • <: Redirects input from a file to a command.
      • sort < files.txt
        • equivalent to sort files.txt
    • &: Used with redirection to signal that a file descriptor is being used.
    • 2>&1: Combine stderr and standard output.
    • 2>file: Redirect standard error to a file.
    • sort < files.txt > sorted_files.txt

  • The Null Device

    • The null device is a special file that throws away whatever is fed to it (aka 'bit bucket')
    • >/dev/null: Redirect output to nowhere.
    • ls 2> /dev/null: Redirect stderr to nowhere (not display on screen)
    • ls here not-here > /dev/null 2>&1: Append stderr to stdoutput

Comparing Files

  • Comparing the Contents of the Files

    • diff file1 file2: Compare two files.
    • sdiff file1 file2: Side-by-side comparison.
    • vimdiff file1 file2: Highlight differences in vim.

  • diff Output

    • In the example below, the third line of the first file is different than the third line in the second file
    • Ouput Syntax: LineNumFile1-Action-LineNumFile2
      • Action = (A)dd/ (C)hange/ (D)elete
 $diff file1 file2
 3c3

 < this is a line from file1
 ---
 > This is a line from file2

  • sdiff Output

    $ sdiff file1 file2
line in file1 | line in file2
            >    more in file2
    • |: Differing lines
    • <: Line from file 1 (only exist in file 1)
    • >: Line from file 2 (only exist in file 2)

  • vimdiff

    • Ctrl-w w: Switch between windows
    • :q: Quit (close current window)
    • :qa: Quit all (close both files)
    • :qa!: Force quit all

Searching in Files and Using Pipes

  • The grep Command

    • grep: Display lines matching a pattern which is case sensitive.
      • Syntax: grep pattern [file]
        • If file is omitted, grep will use the standard input (see section 'Pipes' below)
    • Options
      • -i: Perform a search, ignoring case.
      • -c: Count the number of occurrences in a file.
      • -n: Precede output with line numbers.
      • -v: Invert Match. Print lines that don’t match.

  • The file Command

    • file [file_name]: Display the file type of 'file_name'.
$ file sales.data
sales.data: ASCII text

$ file *
bin: directory
jason.tar: POSIX tar archive

  • Searching for Text in Binary Files

    • strings: Display printable strings

  • Pipes

    • You can chain two commands together with a pipe |
    • Pipe takes the standard output from the preceding command and passes it as the standard input to the following command
    • Syntax: command-output | command-input
    • Example:
      • cat file | grep pattern
        • same as grep pattern file
      • strings giant-steps.mp3 | grep -i john | head -1
      • strings giant-steps.mp3 | grep -i john | head -1 | cut -d' ' -f2

  • The cut command

    • cut [file]: Cut out selected portions of file. If file is omitted, use standard input.
    • Options:
      • -d delimiter: Use delimiter as the field separator.
      • -f N: Display the Nth field.

  • Searching and Pipe Example

    • Find all users named "bob" in /etc/passwd.
      • /etc/passwd contains all accounts in a Linux system
      • grep bob /etc/passwd
      • img
    • Print account name and real name.
      • grep bob /etc/passwd | cut -d: -f1,5
      • img
    • Print in alphabetical order by account name.
      • grep bob /etc/passwd | cut -d: -f1,5 | sort
      • img
    • Print in a tabular format.
      • grep bob /etc/passwd | cut -d: -f1,5 | sort | tr ":" " " img
        • tr "char1" "char2": Translate a character into another character
      • grep bob /etc/passwd | cut -d: -f1,5 | sort | tr ":" " " | column -t img
        • column -t: Format output in table format

  • Piping Output to a Pager

    • more
    • less
      • cat /etc/passwd | less
        • same as less /etc/passwd

Transferring and Copying Files over the Network

  • Copying Files over the Network

    • SCP - Secure copy
    • SFTP - SSH file transfer protocol

  • Command Line SCP Clients

    • scp
    • sftp
    • PuTTY Secure Copy client - pscp.exe (Windows)
    • PuTTY Secure File Transfer client - psftp.exe (Windows)

  • Graphical SCP/SFTP Clients

    • Cyberduck
    • FileZilla
    • WinSCP

  • scp / sftp command line utilities

    • scp source destination: Copy source to destination.
    • sftp host: Start a secure file transfer session with host.
    • sftp jason@host

  • ftp Command Line Utility

    • ftp host: Start a file transfer session with host.
    • FTP is not a secure transfer protocol like SCP and SFTP, use SCP or SFTP over FTP when possible

  • Example: SFTP

    • sftp linuxsvr: Connect to server
    • pwd: When you connect to the remote server, you're placed into your home directory
    • Precede commands with a l, that's for local
      • lpwd
      • lls: Show what files are on the local box
    • put z.txt: Upload file to remote server
    • quit: Disconnect from remote server

  • Example: SCP

    • scp z.txt linuxsvr:/tmp/: Upload file to 'tmp' directory in the remote server
    • scp z.txt linuxsvr:~/: Upload file to remote home directory
    • ssh linuxsvr: Connect to the remote server
    • scp z.txt adminuser@linuxsvr:/home/adminuser/: Transfer file to remote server as a different user
    • sftp adminuser@linuxsvr: Connect to remote server

  • Customizing the Shell Prompt

    • Use an environment variable to customize.
      • Bash, ksh, and sh use $PS1.
      • Csh, tcsh, and zsh use $prompt.
    • Customizing the Prompt with PS1
      • \d: Date in "Weekday Month Date" format "Tue May 26"
      • \h: Hostname up to the first period
      • \H: Hostname (full domain name)
      • \n: Newline
      • \t: Current time in 24-hour HH:MM:SS format
      • \T: Current time in 12-hour HH:MM:SS format
      • \@: Current time in 12-hour am/pm format
      • \A: Current time in 24-hour HH:MM format
      • \u: Username of the current user
      • \w: Current working directory
      • \W: Basename of the current working directory
      • \$: If the effective UID is 0 (root), a #, otherwise a $
    • Persist PS1 Changes
      • Add the PS1 value to your personal initilization file aka 'dot file' e.g. .bash_profile
      • echo 'export PS1="[\u@\h \w]\$ "' >> ~/.bash_profile
      • quit: Log out
      • ssh linuxsvr: Log back in
    • Examples:
      • echo $PS1: Check the current prompt string
      • PS1="\u@\h \$": Customize prompt string
        • Ouput: cabox@box-codeanywhere$
      • PS1="<\t \u@\h \w>\$"
        • Ouput: <10:30:16 cabox@box-codeanywhere ~/workspace>$
      • cd /var/log
      • PS1="\d \t \h \W>\$"
        • Output: Sun Feb 23 09:23:51 linuxsvr log>$

  • Shell Aliases

    • Shortcuts used for long commands andfor commands you type often
    • Creating Aliases
      • Syntax: alias [name[=value]]
        • alias: List aliases set
        • Use name=value to create new alias
    • Fix Typos
      • alias grpe='grep'
    • Make Linux behave like another OS.
      • alias cls='clear'
    • Removing Aliases
      • unalias name: Remove the “name” alias.
      • unalias -a: Remove all aliases
    • Persisting Aliases
      • Add aliases to your personal initialization files e.g. .bash_profile
    • Examples
      • alias ll='ls -l'

Environment Variables

  • An environment variable is a storage location that has a name and a value
  • Environment variables are uppercase by convention

  • Can change how an application behaves

    • See "Environment" section in man pages

  • Viewing Environment Variables

    • printenv: Print all or part of environment.
    • printenv HOME: Print the HOME variable
    • echo $ENV_VAR: Print the ENV_VAR variable.
      • Need to prepend $ when using echo

  • Creating Environment Variables

    • Syntax: export VAR="value"
    • Example:
      • export EDITOR="vi"
      • export TZ="US/Pacific"

  • Removing Environment Variables

    • Syntax: unset VAR
    • Example: unset TZ

  • Persisting Environment Variables

    • Add to your personal initialization files e.g. .bash_profile

  • Common Environment Variables

    • EDITOR: Program to run to perform edits
    • HOME: Home directory of the user.
    • LOGNAME: The login name of the user.
    • MAIL: The location of the user’s local inbox.
    • OLDPWD: The previous working directory.
    • PATH: A list of directories to search for commands.
    • PAGER: Program used to paginate through files.
    • PS1: The primary prompt string.
    • PWD: Present working directory.
    • USER: The username of the current user.

Processes and Job Control

  • Listing Processes and Information

    • ps: Display process status.
    • Options:
      • -e: Everything, all processes.
      • -f: Full format listing.
      • -u username: Display username’s processes.
      • -p pid: Display information for PID.
    • Common ps Commands:
      • ps -e: Display all processes.
      • ps -ef: Display all processes, full.
      • ps -eH: Display a process tree.
      • ps -e --forest: Display a process tree.
      • ps -u username: Display user’s processes.

  • Other ways to view processes

    • pstree: Display processes in a tree format.
    • top: Interactive process viewer.
    • htop: Interactive process viewer.

  • Background and Foreground Processes

    • When a command, process, or program is running in the foreground, the shell prompt will not be displayed until that process exits
    • command &: Start command in background.
    • Ctrl-c: Kill the foreground process.
    • Ctrl-z: Suspend the foreground process.
    • bg [%num]: Background a suspended process.
      • If no parameter, bg will operate on current job i.e. the last job that was stopped while it was in the foreground, or the last job that was started in the background
      • The current job can be referred to by %% or %+
      • The previous job can be refered to by %-
    • fg [%num]: Foreground a background process.
    • kill [%num]: Kill a process by job number or PID.
    • jobs [%num]: List jobs.
      • If not parameter, list all jobs
      • Examples
        • jobs %%: List current job
        • jobs %+: List current job
  • Killing Processes
    • Ctrl-c: Kills the foreground proc.
    • kill [-sig] pid: Send a signal to a process.
      • The default signal used by kill is termination ('TERM')
      • The signal number of 'TERM' is 15 and 'KILL' is 9
      • Examples:
        • kill 123
        • kill -15 123
        • kill -TERM 123
        • if -TERM can't kill, use kill -9 123
    • kill -l Display a list of signals.

Scheduling Repeated Jobs with Cron

  • Cron & Crontab

    • The cron service runs scheduled jobs
    • Use the crontab command to schedule jobs

  • Crontab Format

    • A Crontab or Crontable is a configuration file that specifies when commands are to be executed by Cron
    • Each line in a Crontab represents a job and contains two pieces of infomation:
      • When to run
      • What to run
* * * * * command
| | | | |
| | | | +-- Day of the Week   (0-6)
| | | +---- Month of the Year (1-12)
| | +------ Day of the Month  (1-31)
| +-------- Hour (0-23)
+---------- Minute (0-59)

  • Redirecting Output

    • 0 2 * * * /root/backupdb > /tmp/db.log 2>&1: Run at 02:00 every day and send output to a log file.

  • Example Crontab Entry:

    • 0 7 * * 1 /opt/sales/bin/weekly-report: Run every Monday at 07:00.
    • 0,30 * * * * /opt/acme/bin/half-hour-check: Run every 30 minutes.
    • */2 * * * * /opt/acme/bin/half-hour-check: Another way to do the same thing.
    • 0-4 * * * * /opt/acme/bin/first-five-mins: Run for the first 5 minutes of the hour (run 5 times every hour)

  • Crontab Shortcuts

    • This may or may not work on your Linux distribution. Use man cron to check if this works for you
    • @yearly 0 0 1 1 *
      • at midnight on the morning of Jan 1
    • @annually 0 0 1 1 *
      • same as @yearly
    • @monthly 0 0 1 * *
      • at midnight on the morning of the first day of the month
    • @weekly 0 0 0
      • at midnight on the morning of Sunday
    • @daily 0 0 * * *
      • at midnight
    • @midnight 0 0 * * *
      • same as @daily
    • @hourly 0 * * * *

  • Using the Crontab Command

    • The crontab command manipulates cron jobs
    • crontab file: Install a new crontab from file.
    • crontab -l: List your cron jobs.
    • crontab -e: Edit your cron jobs.
      • Will invoke the editor that's specified in the 'EDITOR' environment variable
    • crontab -r: Remove all of your cron jobs.

Switching Users and Running Commands as Others

  • The su Command

    • su [username]: Switch user
      • If no arguments supplied, su assumes you try to become a superuser (root)

  • su Options

    • -: A hyphen is used to provide an environment similar to what the user would expect had the user logged in directly.
      • For example, environment variable 'TEST' created by userA will not be available to userB using the su - userB option
    • -c command: Specify a command to be executed.
      • su -c 'echo '$ORACLE_HOME' - oracle

  • Who Am I?

    • whoami: Displays your account name.
    • Example:
$whoami
jason
$ su oracle 
Password:
$ whoami
oracle
$
  • Sudo - Super User Do
    • sudo: Execute a command as another user, typically the superuser.
    • One of the advantages of using sudo over the su command is that you don't need to know the password of the other user. If the sudo configuration permits access, that command is executed
    • Using sudo:
      • sudo -l: List available commands.
      • sudo command: Run command as root.
      • sudo -u root command: Same as sudo command.
      • sudo -u user command: Run as user.
      • sudo su: Switch to the superuser account.
      • sudo su -: Switch to the superuser account with root’s environment.
      • sudo su - username: Switch to the username account.
      • sudo -s: Start a shell
      • sudo -u root -s: Same as sudo -s
      • sudo -u user -s: Start a shell as user
    • Changing the sudo Coniguration
      • visudo: Edit the /etc/sudoers file
      • Requires root privileges to run
    • Sudoers Format
      • Syntax: user host=(users) [NOPASSWD:]commands
      • Examples:
        • adminuser ALL=(ALL) NOPASSWD:ALL
        • jason linuxsvr=(root) /etc/init.d/oracle

Shell History and Autocompletion

  • Shell History

    • Executed commands are added to the history
    • Shell history can be displayed and recalled
    • Shell history is stored in memory and on disk (on exit)
      • History files are stored in 'home' directory:
        • ~/.bash_history
        • ~/.history
        • ~/.histfile

  • history Command

    • history: Display the shell history.
    • HISTSIZE: Controls the number of commands to retain in history.
      • By default, bash retains 500 commands in your shell history
      • export HISTSIZE=1000: Increase history size
        • Place that in your personal initialization file

  • ! Syntax

    • !num: Repeat command line number 'num'.
      • Use history to view the line number
      • ! is called "bang"
    • !!: Repeat the previous command line.
      • Also called "bang bang"
    • !string: Repeat the most recent command starting with "string."
    • !^: Represents the first argument
      • !^ = !:1

    • !$: Represents the last argument

    • Pulling Out Words from Previous Command

      • Syntax: !:num <Event> <Separator> <Word>
        • !: Represents a command line (or event).
          • !: The most recent command line
          • !=!!
        • :num: Represents a word on the command line
          • 0: command
          • 1: first argument, etc.
      • Examples
$ head files.txt sorted_files.txt notes.txt
<output from head command here>

$ !!
head files.txt sorted_files.txt notes.txt
<output from head command here>

$vi !:2
vi sorted_files.txt
<vi editor starts>

$ls !^
ls files.txt
<output from ls here>

$ls !$
ls notes.txt
<output from ls here>

  • Searching Shell History

    • Ctrl-r: Reverse shell history search
      • Press Ctrl-r again to get to next match
    • Enter: Execute the command
    • Arrows: Change the command
    • Ctrl-g: Cancel the search

  • Auto Completion

    • Tab: Perform auto completion
    • Tab+Tab: View all the possible completion options
    • Works on files, directories, paths, environment variables, usernames(~)
      • ls -ld ~: list current user home directory
      • ls -ld ~adm: list user home directory starts with 'adm'
        • Output: ~adm ~adminuser/

Installing and Managing Software

  • Package

    • A package is a collection of files that makes up an application
    • A package contains Data / Metadata such as:
      • Package description
      • Version
      • Dependencies

  • Package Manager

    • Installs, upgrades, and removes packages
    • Manages dependencies
    • Keeps track of what is installed
    • Installing or removing package requires root priviledges
      • Use sudo or su to the "root" user if sudo is not configured

  • Installing Software on RPM Distros

    • RPM stands for "Redhat Package Manager"
      • RedHat
      • CentOS
      • Fedora
      • Oracle Linux
      • Scientific Linux
    • yum
      • The yum command line utility is a package management progrm for those Linux distributions that use RPM packages
      • yum search string: Search for package containing 'string'
      • yum info [package]: Display info
      • yum install [-y] package: Install package
        • Use -y to automatically reply 'yes' to yum's questions
      • yum remove package: Remove package
    • rpm
      • rpm -qa: List all installed packages.
      • rpm -qf /path/to/file: List the file’s package.
      • rpm -ql package: List package’s files.
      • rpm -ivh package.rpm: Install package.
      • rpm -e package: Erase (uninstall) package.

  • Installing Software on DEB Distros

    • DEB stands for "Debian"
      • Debian
      • Linux Mint
      • Ubuntu
    • APT
      • APT stands for "Advanced Packaging Tool"
      • apt-cache search string: Search for package with 'string'.
      • apt-get install [-y] package: Install package.
        • Use -y to automatically reply 'yes' to apt-get's questions
      • apt-get remove package: Remove package, leaving configuration.
      • apt-get purge package: Remove package, deleting configuration.
      • apt-cache show package: Display information about package.
    • dpkg
      • dpkg -l: List installed packages.
      • dpkg -S /path/to/file: List file’s package.
      • dpkg -L package: List all files in package.
      • dpkg -i package.deb: Install package.

Addendum: Connecting to a Linux Virtual Machine (VM) over the Network

  • Stops any VM that is running

  • Make sure that the network adaptor is set to "Bridged" img

  • Starts the VM

  • Make sure that a ssh-server is installed and running

    • ps -ef | grep sshd: Check process table and search for SSH daemon / SSH server process

    • The results show that sshd is not running img

    • Check if ssh-server is installed

      • DEB: dkpg -l | grep ssh-server
      • RPM: rpm -qa | grep ssh-server

    • If not found, install ssh-server

      • DEB:
        • sudo apt-get update
        • sudo apt-get install openssh-server openssh-client
          • openssh-client is used to connect to other system from this system
      • RPM:
        • sudo yum install openssh-server openssh-client

  • Look at the process table and check for sshd, make sure it's running

    • ps -ef | grep sshd

    • You can see that it's up and running img

    • If not running, use

      • DEB: sudo service ssh start
      • RPM: sudo service sshd start

  • Get the IP address of this VM

    • /sbin/ip addr

    • Note there are 2 network interfaces img

      • The 1st network interface is a virtual network interface that will be present on all systems.
      • Called the loopback device which allows the system to communicate with itself
      • Always has an ip address of 127.0.0.1
      • Use the ip address 10.0.0.6 in the 2nd network interface

  • Confirm username

    • whoami
    • For security reason, SSH access is usually disabled for the root user. If so, use other username to connect instead

  • Connect to VM using Terminal

    • From Linux & Mac
      • ssh adminuser@10.0.0.6: Login VM
      • exit: Exit VM
    • From Windows
      • putty: Starts putty